[API] RT-37785 Provide some useful TextInputControl.Formatter implementations

[Martin Sladecek]

Hello,
as RT-14000 (https://javafx-jira.kenai.com/browse/RT-14000) - text 
formatter for TextInputControl has been pushed recently, it's time to 
discuss what implementations of Text Formatter should be included in 
8u40 release.

I added some ideas to (https://javafx-jira.kenai.com/browse/RT-37785), 
where all the comments should go.

Here's some short summary:
* StringFormatter for converting between String and arbitrary object 
using toString and valueOf (or String constructor), which would do 
similar job as DefaultFormatter in swing.
* MaskFormatter (similar to the class of the same name in swing) - it 
would support String mask, defining own placeholder character, escape 
character or even defining own map (as a Map<Character, 
UnaryOperator<Character>>), where the unary operator for the map either 
returns null (if not accepted) or the same/modified character if accepted.
* A TextFormatter that takes java.text.Format and does the filtering and 
converting using the Format object.

Thanks,
-Martin